A Radio Frequency (RF) measurement system is one that measures something about a Device Under Test (DUT) by sampling and measuring signals applied to and coming from the DUT. A vector measurement system will measure both magnitude and phase information, while a scalar measurement system will measure magnitude only.
In this document, a “tuner system” or “impedance tuner system” will refer to a RF measurement system which uses some kind of tuner or tuners to control impedance seen by the DUT.
An “automated tuner” may be computer controlled; a “manual tuner” is controlled manually by the user. Automated tuners are commercially available, for example, model MT982EU30 by Maury Microwave Corporation.
There are various types of impedance tuners. A slide screw tuner includes a transmission line in some media, such as coaxial, slabline, waveguide, microstrip, etc. One or more probes can move perpendicular to the center conductor. As a probe moves closer to the center conductor, the mismatch at some frequency will increase, while the mismatch decreases as the probe moves away from the center conductor. At some point, when the probe is far enough away, it has very little effect on the fields around the center conductor, so the transmission line looks nearly like a uniform line without a deliberate mismatch. A solid state tuner has multiple solid state elements which are controlled to effect impedance variation, e.g. a number of PIN diodes, FETs or other solid state devices coupled to a transmission line. Impedance variation is achieved by applying DC control signals to bias individual solid state elements or a combination of solid state elements. In the case of PIN diodes, the diodes are biased in either the forward or reverse direction.
The electronically-controlled tuner systems are controlled by providing signals to cause the impedance-varying elements to assume a particular state or position.